fix cdn javadoc wrt configuration

Author: netomi

server/src/main/java/org/eclipse/openvsx/storage/CdnServiceConfig.java

@@ -30,7 +30,7 @@
  *     cdn:
  *       enabled: true
  *       services:
- *         - aws: https://my.cdn.front.domain/
+ *         aws: https://my.cdn.front.domain/
  * </pre>
  */
 @Configuration